1. Field of the Invention
The present invention relates generally to computer data storage and retrieval, and more particularly, to recording media format structures and the associated control logic process for recording and retrieving data with said format structures. More specifically, the present invention relates to data recording in such a manner as to organize data blocks into constructs that optimize performance criteria.
2. Description of the Related Art
From the start, digital computers have required some form of data storage to augment the relatively sparse main memory facilities. Magnetic and optical recording media provides such non-main memory storage means in the state of the art. Many forms of recording media drives, using technologies such as cassettes or cartridges, reel-to-reel tape, digital audio tape, eight millimeter tape, magneto-optical and optical disks, flash RAM, and other media, are now available in the market.
A goal of data storage and retrieval technology developers is to maximize the defining of units of readily accessible and identifiable, or "addressable," blocks of recorded information (which may be an application or utility computer program, modules, user data, or the like, collectively referred to hereinafter as "data").
For example, personal computers are generally equipped with a floppy disk controller printed circuit board and disk drive for retrieval (e.g., loading software onto the hard disk main memory of the computer) or storage (namely, hard disk backup or archiving of data). However, floppy disk capacity is limited in the state of the art to approximately twenty-one megabytes per 31/2 inch form factor diskette. With common personal computers having a hard drive of more than two-hundred megabytes, the use of floppy disks for data back UP or archiving is impractical. Therefore, other recording machines such as magnetic tape and optical disk have been developed and are increasing in popularity.
Magnetic tape devices have found popularity as fast, efficient, and economical means for storing computer data. Tapes are used primarily for such tasks as routine back up of a hard disk and for off-line file management tasks routinely implemented between a computer hard disk memory and tape as data is processed.
Streaming tape drives (also referred to as "streamers") operate similarly to disk drives in that they are constant speed transports for storing data from computers, that is, once started, the drive moves the tape from its physical beginning to its physical end, or vice versa, whether or not there is data to record. Data is transferred to a drive apparatus which uses a cartridge or cassette containing the recording medium. Streaming drives generally record unidirectionally, laying down as many parallel tracks as tape, head, and drive electronics technology will permit. However, some streamers are capable of writing bidirectionally; upon reaching the defined end of the media, the drive selects a different set of tracks, reverses the relative motion of the medium with respect to the head, and writes on the newly selected set of tracks. This method is known in the art as "serpentine recording." Thus, the conventional serpentine recording format schemes write data in a single, lengthy data stream on multiple tracks along the full length of the tape. Magnetic tape media in a cartridge such as that set forth in the ANSI X3.55-1992 Standard or U.S. Pat. No. 3,692,255, Belt Drive Tape Cartridge (incorporated herein by reference), used in such recording is adaptable for use with the present invention.
A general description of computer tape drive technology can be found in the book STREAMING, Copyright 1982, Archive Corporation, Library of Congress Catalog No. 82-072125, incorporated herein by reference. Industry standards for recording with streamers on 1/4-inch wide magnetic tape are promulgated by the Quarter Inch Cartridge ("QIC") Committee and are commonly referred to as "QIC Standards."
Various modes of recording using such drives have been created, for example, longitudinal (stop-start or back-hitch recording), helical scanning, and streaming. One example of a serpentine mode recording, streaming tape drive that provides an alternative recording mode is disclosed by Precourt in U.S. Pat. No. 5,541,019, Recording System for Recording Data on Tape in a Disk-Recording Format. Precourt discloses an apparatus in which the elements of a floppy disk format (that is, circular disk tracks and sectors that comprise a disk track, known in the art as Fixed Block Architecture disk format) are imposed on a data stream sent to a serpentine recording tape drive. In general, the command set for disk recording is interpreted to give the appearance that data recorded on tape is recorded on a magnetic disk by using the floppy disk controller. As shown in FIG. 5 of Precourt, the stream of data presented to the tape drive is divided into records called segments. Each recorded segment 120 includes a first fill field 121, followed by a predetermined number of fields called sectors 1, 2 . . . n, including identifying addresses and data, followed by a second fill field 122 until an end-of-segment index pulse is provided by a controlling microprocessor to the host. The segment length in the data stream is equivalent to the number of data bytes necessary to store the data that defines the length of a concentric track on a floppy disk. Thus, Precourt teaches manipulation of a stream of data presented to a serpentine recording tape drive emulating a floppy disk drive, but does not address the definition of the actual data format for a tape or disk drive nor provide improved constructs that optimize performance criteria.
A more common means used in QIC streaming tape drives for tracking and retrieving data once it is recorded is disclosed by Mintzlaff in U.S. Pat. No. 4,858,039, Streaming Tape Drive With Direct Block Addressability. By calculating the difference between the address of the current data bock at the read-write head and the address of the desired data block address on the tape, a control algorithm steps directly to the desired serpentine track and then streams to the desired data block. Thus, data block access time is reduced from a strictly serial search of the tape to a process of stepping to the desired track and then performing a serial search of that track for the desired data block. Again, Mintzlaff's invention does not address the subject of the current invention which is used to define the actual media format for a tape or disk drive nor provide the accompanying advantages.
While removable recording media has the desirable characteristic of being inexpensive enough to store large data bases in their entirety, it is also limited in application due to the latencies (defined by the McGraw-Hill Dictionary of Scientific and Technical Terms, 4th Ed., copr. 1989 as: "[COMPUT SCI] The waiting time between the order to read/write some information from/to a specified place and the beginning of the data-read/write operation") associated with media handling and positioning. Such latencies can limit storage and retrieval job throughput. These latencies include mechanical related factors, such as loading and unloading the media, seeking, serial bock searching, rewinding, or system related timing factors such as media initialization, directory searching, or file label reading.
Therefore, there is a need for a recording technique that provides higher performance for the host computer.